Geographical-clock dial



v (No Model.) 3 Sheets-Sheet 1.

D. W. THOMPSON.

GEOGRAPHICAL CLOCK DIAL. No. 557,173. Patented Mar.31,1896.

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ANDREW BGRAHAM. PHOTOUMQWASHINGTDN. ILC

(No Model.) 3 SheetS Sheet 2 D. W. THOMPSON.

GEOGRAPHICAL CLOCK DIAL. No. 557,173. Patented M31231, 1896.

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WITNESSES: INVENTOH A TTOHNEYS.

ANDREW EGHAHAM. PHOTO'LITHD. WASHI N emu D c.

3 Sheets-Sheet 3.

(No Model.)

D. W. THOMPSON.

GEOGRAPHICAL CLOCK DIAL.

Patented Mar. 31, 1896 lNl/E/VTOH J. I barn 17am;

WITNESSES.

BY W

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lNDREW 8.6RAHAM. PHDTO-LITHO. WASKIN FI'O'LDL.

UNITED STATES PATENT OFFICE.

DAVID IV. THOMPSON, OF ENGLEWOOD, ILLINOIS.

GEOGRAPHICAL-CLOCK DIAL.

SPECIFICATION forming part of Letters Patent No. 557,173, dated March31, 1896.

Application filed February 18,1893. Renewed August 28, 1895. Serial No.560,820. (No model.)

To all whom it may concern:

Be it known that 1, DAVID IV. THOMPSON, of Englewood, in the county ofCook and State of Illinois, have invented a new and useful Improvementin'Universal Diurnal and Geographical Clocks, of which the following isa specification,

The object of my invention is to provide for the use of educationalinstitutions a clock that will indicate to the eye, in addition to thelocal time of the place, the time of day or night in all parts of theworld, the portion of the earths surface where daylight prevails and theportion where night prevails, and capable of adjustment to illustratethe same for all seasons of the year and all latitudes, and which shallalso illustrate to the eye the rising and setting of the sun in alllatitudes and seasons of the year, showing where, when, and why sixmonths day and six months night prevail near the poles, the summer andwinter solstices, the autumnal and vernal equinoxes, and, in fact, allterrestrial phenomena dependent upon the inclination of the earths axisto the ecliptic and the revolution of the earth.

To these ends my invention consists of an artificial shadow or screen,the form of which can be changed or adjusted to correspond to the shapeof the shadow at all seasons of the year, in combination with a map ofthe circumpolar hemisphere divided into hours of longitude and connectedto rotate with the hour-hand of a twenty-four-hour clock whose dial isnumbered in two consecutive series of figures from 1 to 12, torepresent-the twelve hours of day and twelve hours of night, all ashereinafter more fully described.

Figure 1 is a face view of a clock constructed in accordance with myinvention equipped for the northern hemisphere and arranged for rotationreversely to the ordinary motion of a clock. Fig. 2 is a similar view ofa clockface equipped for the southern hemisphere with the hands arrangedto rotate in the opposite direction or usual way. Fig. 3 is a sectionthrough line a; o: of Fig. 1. Fig. 4 shows a series of the shadow-platesmarked to inclicate the month united as a continuous strip or ribbon,and Fig. 5 shows how these may be arranged in the clock upon rolls.

Referring to Fig. 1, A represents the dial of a tWentyfour-hour clock,which is numbered in two series of figures from l to 12 following eachother and progressing in direction reverse to that of the ordinaryclock.

B is the hour and O the minute hand of the clock, which are geared inthe usual way, ex cept that the hour-hand revolves but once (and nottwice, as usual) in the twenty-four hours. To the hour-hand is attachedconcentrically to move with it a disk D, upon which is delineated thecircumpolar hemisphere representing in Fig. 1 the northern half of theearths surface. This map is divided by radial lines from the pole intodivisions of longitude representing fifteen degrees each, which arenumbered progressively both ways for east and west longitude from 0 onone side of the earth to 180 on the opposite side, the numbersincreasing by fifteen degrees. The spaces between these divisions oflongitude are fifteen degrees, each of which represents in therevolution of the earth just one hour of time, so that these spaces orlongitude-lines are correlated to the twenty-four hour subdivisions ofthe dial to couple the subdivisions of time with the various localitieson the map.

E is a plate of semitransparent material, such as colored mica, horn,celluloid, or other similar substance which can be made to represent theshadow or shaded portion of the earths surface to indicate night andstill be sufficiently transparent to allow the localities on the map tobe read through the same. This artificial or representative shadow isfixed to the face of the clock, so as to be sta tionary, and yet is madedetachable, so as to permit other shapes of shadow to be substituted,for it will be understood that such shadow will only appear semicircularwith a straight diameter at the two periods of the year, representingthe vernal and autumnal equinoxes. At other times it will be greater orless than a semicircle, dependent upon the angle of the ecliptic andwhich end of the earth is turned toward the observer.

Referring to Fig. 1, it will be perceived that the side of the earthcontaining the western hemisphere is turned toward the sun, and overthat area it is day, while upon the opposite side, covered by the screenor shadow, it is night. The junction of the line of light and darknessis, as shown, a straight diametrical line, and with the earth turning inthe direction of the arrow the line represents on the left morning wherethe earth is turning into the light, while upon the right, where theearth is turning out of the light and into the shadow, it is evening ortwilight. Midway between these points on the light side it is noon, andat a diametrical point on the shadow it is midnight.

Now to know what time of day or night it is at any point on the earthssurface it is only necessary to extend radially the longitudeline of theplace to the outer figures of the clock-dial,whether it be in the shadowor light, the apportionment of the longitude of the earth in hoursubdivisions (fifteen degrees) to correspond with the twenty-fournumbers permitting this to be instantly observed without calculation. Toenable the eye to follow the radial position of the clock-dial figuresinward across the surface of the earth, the glass face G of the clockshould have radial lines engraved or etched thereon and con verging fromthe several twenty-four marks inwardly to the pole.

lVhen the day and night are equal, the line separating the light anddark side of the earth will be a straight diametrical line passingthrough the poles as in Fig. 1, which occurs at the periods of vernaland autumnal equinox. At other times one pole will be a region ofcontinual day and the other one of continual night for a period of sixmonths. This is due tothe angle of the earths axis,

. or the ecliptic, which holds one pole toward the sun through thecomplete revolution of the earth and the other in the shadow for thesame length of time. To illustrate this, I now refer to Fig. 2,whichshows the southern hemisphere, in which the map revolves in the usualdirection of the clock-hands and in which the shadow is shown in theposition of summer and winter solstice. As shown, the south pole iswholly within the light and there is no night for six months. The dottedcurved line shows the position of the shadow after six months haveelapsed and the movement of the earth in its orbit has reversed theangle of the ecliptic, and which shows the south pole continually in theshadow for six months.

In the use of my invention I prefer to append the ordinary hour andminute hands; but it is obvious that these are not essential features ofmyinvention, since the geographical location by radiating lines oflongitude constitute so many pointers to the several twenty-four hou sof the clock-dial as to be sufficient, and the hour and minute hands areonly put on to enable the observer to note his local time by easy effortat a more or less remote point from the clock.

In Fig. 3 are shown the different planes which the several features ofthe clock-dial occupy. The shadow-plates are constructed as a continuousstrip or ribbon, as in Fig. 4, which is arranged upon rolls, as in Fig.5, to be fed successively across the face of the dial to illustrate thedifferent phases of the shadow.

The dial may be used without an actuatingtimepiece and without hands asan educational chart, and in such case it will be contained in a frame,as indicated in dotted lines in Fig. 1, and a notch n will allow accessto the periphery of the map to rotate it, or any other means forrotating it may be used.

I am aware that it is not broadly new to apply a circumpolar map to aclock-dial having twenty-four hour subdivisions and that twoshadow-plates have been applied to the opposite ends of arectilinearly-moving Mercators map, and I do not claim either of thesearrangements. By applying the single shadow-plate to onehalf of thecircumpolar map a single plate is made to indicate a complete cycle ofday and night in a very simple, practical, correct, and graphic way, andI am enabled also to indicate the different phases of the night-shadowsalong its edge.

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent, is-

The combination with a circumpolar map made revoluble about a centralaxis; of a series of movable material representations of the shadowedportion of the earths surface applied to one-half of said map, and madein the form of a continuous strip having along its edge different shapescorresponding to and indicating the different phases of the earthsshadow, and means for sustaining the same substantially as shown anddescribed.

DAVID XV. THOMPSON. Vitnesses:

EDwD. W. BYRN, J. l\IIDDLETON.

